(a) Field of the Invention
The present invention relates to a technique of manufacturing a plane coil, and more particularly relates to a method of manufacturing a plane coil composed of a conductor wound in a spiral substantially on a plane.
(b) Description of the Related Art
In non-contact type IC cards, IC tags, and the like, a plane coil is used as an antenna for communicating information between an embedded semiconductor element (IC) and an external card processing apparatus or the like. Conventionally, such a plane coil has been formed by winding a coated wire or by etching or stamping a metal plate.
A method using a coated wire requires a step of interweaving or embedding a wound coil into a support base material in order that the wound coil holds a required shape of antenna. However, the coated wire for use is an inelastic thin wire, so that the coated wire is difficult to wound and not suitable for mass processing. Moreover, since this method requires the step of interweaving the wound coil or the like after the winding, it has a disadvantage in that a manufacturing cost thereof is increased. Thus, it has been difficult for the method of manufacturing a plane coil by winding a coated wire to achieve a reduction in cost and a mass production.
On the contrary, a method of manufacturing a plane coil by etching or stamping is more advantageous than the above method by winding a coated wire, in terms of cost, mass production, and manufacturing period. In an example of the method using etching, a metal foil or sheet is pressed and stuck on an insulative support base material (film of heat-resistant resin such as polyethylene terephthalate (PET)), and a surface on which the metal foil or the like is stuck is then etched to be formed in a required shape of coil.
On the other hand, in an example of the method using stamping, a metal sheet is stamped in a shape of a pattern in which coils (antennas) are partly connected to each other, and a support base material such as a PET film is stuck onto the stamped metal sheet, with keeping the stamped shape, and then, joining portions which partly connect the coils are cut off. In this case, in a conventional method of attaching the PET film, hot melt resin is coated on a surface (on a side to be brought into contact with the metal sheet) of the PET film which is being unwound and conveyed from a winding body on which the PET film is wound in a roll. The PET film is then stuck onto the metal sheet with this hot melt resin interposed therebetween. Herein, the hot melt resin is provided with a sticking property by heating.
As described above, the method of manufacturing a plane coil by etching or stamping a metal sheet is more advantageous than the method of manufacturing a plane coil by winding a coated wire, in terms of cost, mass production, and the like. Comparing the method using etching with that using stamping, the former is more disadvantageous than the latter because of higher manufacturing cost.
On the other hand, the method using stamping employs hot melt resin when sticking the PET film (support base material) onto the stamped metal sheet as described above, and thus has a problem in that the manufacturing cost is increased by use of the hot melt resin.
The applicant has already proposed a technique of coping with such a problem (Japanese Patent Application No. 2002-288628 filed on Oct. 1, 2002). In the proposed technique described in the specification and drawings, a sheet member (in which a metal foil is stuck on a surface of an insulative support sheet with a pressure-sensitive adhesive interposed therebetween) is used as a starting material for manufacturing a plane coil, and the sheet member is in advance wound on a reel in a roll. The sheet member which is being unwound and conveyed from the reel is stamped in a required shape of coil. After the stamped metal foil (coils) is stuck onto a base film such as a PET film (after transferred and laminated), unnecessary joining portions between the coils are cut off. In the proposed technique, a plane coil is manufactured by using a seal material which is easily commercially available at comparatively low cost, and applying a stamping technique. Accordingly, it is possible to achieve a reduction in the manufacturing period as well as a reduction in cost and a mass production.
However, this method uses a metal foil with a very small thickness as the material forming the coils, and the conductor width (line width) of the spiral coil is extremely small. Accordingly, the rigidity of the coil (metal foil) cannot be maintained, and it is difficult to transfer/laminate the coil onto the base film with keeping the shape of the stamped coil. Therefore, it can be supposed that a coil will be deformed, a part of the coil will be cut off depending on the conditions, or adjacent conductors in the coil will be brought into contact with each other (short-circuited between each other). Consequently, a reliability of the plane coil as a finally obtained product is lowered, and thus there is room for improvement in this respect.